Prepare to say good-bye to Pretty Little Liars as you know it! According to executive producer Marlene King, the hit ABC Family series will undergo a change so drastic at the end of Season 5, it might be unrecognizable to fans.

"There is a twist towards the end that is by far our most demented and mind-boggling," she told BuzzFeed News via phone. "I have goosebumps just thinking about it. We take a shocking turn and everyone was like, 'Wow, I can't believe this is the show now.'"

But before Pretty Little Liars gets to that shocking season ender, there are still 12 episodes remaining in Season 5 (the second half of which premieres on Jan. 6) and here's an exclusive look at what's to come.

ABC Family

The first half of Season 5 ended with Mona's (Janel Parrish) brutal murder, which King said is a shot of adrenaline straight to the heart of Pretty Little Liars. "It really jumpstarts the rest of the show," she said, adding that the Liars focus all their attention on identifying Mona's murderer — a task that's of particular interest to Hanna (Ashley Benson). "She has a lot of guilt," King said of the former pair of best friends. "She really wants to avenge Mona's death."

The girls will get help from beyond the grave as they continue to feel Mona's presence in Rosewood. "When I called Janel to tell her that Mona was about to meet her demise, I reassured her that, in the same way Sasha [Pieterse, who plays the Liars' presumed-to-dead-but-actually-alive friend Alison DiLaurentis] has been in the show — and such a strong part of the show, from the beginning, as a dead girl — that's the role Mona's going to take," King said.

Plus, in true Mona fashion, she's left behind some clues for the Liars. "As it turns out, Mona had a plan B in the event of her demise," King revealed. "The Liars are gifted with a treasure map that may help them put the pieces together so they can solve the mystery of who killed Mona."

And the Liars won't be the only ones jumping into the "A" fray this season. King revealed that Aria (Lucy Hale), Spencer (Troian Bellisario), and Hanna's boyfriends — Ezra (Ian Harding), Toby (Keegan Allen), and Caleb (Tyler Blackburn) — take on bigger roles in trying to vanquish Rosewood's hooded blackmailer — although that's not good news for all three fan-favorite couples.

"As a police officer, Toby is going to use his position to really get deeply involved in this investigation," King said. "Interestingly, instead of it bringing Spencer and Toby closer together, it has a way of keeping them separated."

In fact, going separate ways is a major theme for all of the girls in the second half of Season 5. "Their game plan is, I have to get into college so I can get the hell out of here. Let's split up four ways so there's no way 'A' can find all of us," King said, adding that the looming deadline presents a unique problem for Ezria. "Aria is really concentrating on, How do I get into college? How do I get out of here? Do I bring Ezra with me? And if I do, what does that look like?"

And those visions of their "A"-free futures lead the girls in very different and extreme directions. "The girls make a decision in 5B that they haven't been willing to in the past," King revealed. "They'll stand together against an evil they haven't been able to face in the past. This season gets a little darker and it gets a little more dramatic. It's extremely high stakes."